1. Field of the Invention
The present invention relates to a thin film magnetic head having at least an inductive-type magnetic transducer for writing and a method of manufacturing the same.
2. Description of the Related Art
Performance improvement in thin film magnetic heads has been sought in accordance with an increase in surface recording density of a hard disk device. A composite thin film magnetic head, which is made of a layered structure including a recording head having an inductive-type magnetic transducer for writing and a reproducing head having magnetoresistive (MR) elements for reading, is widely used as a thin film magnetic head. The MR elements includes an anisotropic magnetoresistive (AMR) element that utilizes the AMR effect and a giant magnetoresistive (GMR) element that utilizes the GMR effect. A reproducing head using an AMR element is called an AMR head or simply an MR head. A reproducing head using the GMR element is called a GMR head. The AMR head is used as a reproducing head whose surface recording density is more than 1 gigabit per square inch. The GMR head is used as a reproducing head whose surface recording density is more than 3 gigabit per square inch.
In general, an AMR film is made of a magnetic substance that exhibits the MR effect and has a single-layered structure. In contrast, most of GMR films have a multi-layered structure consisting of a plurality of films. There are several types of mechanisms which produces the GMR effect. The layer structure of a GMR film depends on the mechanism. The GMR films include a super-lattice GMR film, a spin valve film, a granular film and so on, while the spin valve film is most efficient as the GMR film which has a relatively simple structure, exhibits a great change in resistance in a low magnetic field, and is suitable for mass reproduction.
As a primary factor for determining the performance of a reproducing head, there is a pattern width, especially an MR height. The MR height is the length (height) between the end of an MR element closer to an air bearing surface and the other end. The MR height is originally controlled by an amount of grinding when the air bearing surface is processed. The air bearing surface (ABS) here is a surface of a thin film magnetic head that faces a magnetic recording medium and is also called a track surface.
Performance improvement in a recording head has also been expected in accordance with the performance improvement in a reproducing head. It is required to increase the track density of a magnetic recording medium in order to increase the recording density among the performance of a recording head. In order to achieve this, a recording head of a narrow track structure in which the width of a bottom pole and a top pole sandwiching a write gap on the air bearing surface is required to be reduced to the order of some microns to submicron. Semiconductor process technique is used to achieve the narrow track structure.
Another factor determining the performance of a recording head is the throat height (TH). The throat height is the length (height) of a portion (magnetic pole portion) which is from the air bearing surface to an edge of an insulating layer which electrically isolates the thin film coil. Reducing the throat height is desired in order to improve the performance of a recording head. The throat height is controlled as well by an amount of grinding when the air bearing surface is processed.
In order to improve the performance of a thin film magnetic head, it is important to form the recording head and the reproducing head as described in well balance.
Here, an example of a manufacturing method of a composite thin film magnetic head as an example of a thin film magnetic head of a related art is to be described with reference to FIGS. 31A and 31B to FIGS. 36A and 36B.
As shown in FIGS. 31A and 31B, an insulating layer 102 made of, for example, alumina (aluminum oxide, Al.sub.2 O.sub.3) of about 5 to 10 .mu.m in thickness is formed on a substrate 101 made of, for example, aluminum oxide and titanium carbide (Al.sub.2 O.sub.3.multidot.TiC). Further, a bottom shield layer 103 for a reproduction head made of, for example, permalloy (NiFe) is formed on the insulating layer 102.
Next, as shown in FIGS. 32A and 32B, for example, alumina of about 100.about.200 nm in thickness is deposited on the bottom shield layer 103 to form a shield gap film 104. Then, an MR film 105 of tens of nanometers in thickness for making up the MR element for reproduction is formed on the shield gap film 104, and photolithography with high precision is applied to obtain a desired shape. Next, a lead terminal layer 106 facing the MR film 105 is formed by lift-off method. Next, a shield gap film 107 is formed on the shield gap film 104, the MR film 105 and the lead terminal layer 106, and the MR film 105 and the lead terminal layer 106 are buried in the shield gap layers 104 and 107. Next, a top shield-cum-bottom pole (called bottom pole in the followings) 108 of about 3 .mu.m in thickness made of, for example, permalloy (NiFe), which is a material used for both of a reproduction head and a recording head, is formed on the shield gap film 107.
Next, as shown in FIGS. 33A and 33B, a write gap layer 109 of about 200 nm in thickness made of an insulating layer such as an alumina film is formed on the bottom pole 108. Further, an opening 109a for connecting the top pole and the bottom pole is formed through patterning the write gap layer 109 by photolithography. Next, a pole tip 110 is formed with magnetic materials made of permalloy (NiFe) and nitride ferrous (FeN) through plating method, while a connecting portion pattern 110a of the top pole and the bottom pole is formed. The bottom pole 108 and a top pole layer 116 which is to be described later are connected by the connecting pattern 110a and so that forming a through hole after CMP (Chemical and Mechanical Polishing) procedure which is to be described later becomes easier.
Next, as shown in FIGS. 34A and 34B, the write gap layer 109 and the bottom pole 108 are etched about 0.3.about.0.5 .mu.m by ion milling having the pole tip 110 as a mask. By etching the bottom pole 108, a trim structure is formed. As a result, widening of effective write track width can be avoided (that is, suppressing widening of magnetic flux at the bottom pole when data is being written). Next, after an insulating layer 111 of about 3 .mu.m, made of, for example, alumina is formed all over the surface, the whole surface is flattened by CMP.
Next, as shown in FIGS. 35A and 35B, a first layer of a thin film coil 112 for inductive-type recording heads made of, for example, copper (Cu) is selectively formed on the insulating layer 111 by, for example, plating method. Further, a photoresist film 113 is formed in a desired pattern on the insulating layer 111 and the thin film coil 112 by photolithography with high precision. Further, a heat treatment of desired temperature is applied for flattening the photoresist film 113 and insulating between the thin film coils 112. Likewise, a second layer of a thin film coil 114 and a photoresist film 115 are formed on the photoresist film 113, and a heat treatment of desired temperature is applied for flattening the photoresist film 115 and insulating between the thin film coils 114.
Next, as shown in FIGS. 36A and 36B, a top pole yoke-cum-top pole layer (called a top pole layer in the followings) 116 made of, for example, permalloy, which is a magnetic material for recording heads, is formed on the top pole 110, the photoresist films 113 and 115. The top pole layer 116 has a contact with the bottom pole 108 in a position rear of the thin film coils 112 and 114, and is magnetically coupled to the bottom pole 108. Further, an over coat layer 117 made of, for example, alumina is formed on the top pole layer 116. At last, a track surface (air bearing surface) of recording heads and reproducing heads is formed through a slider machine processing, and a thin film magnetic head is completed.
In FIGS. 36A and 36B, TH represents the throat height and MR-H represents the MR height. Further, P2W represents the track (magnetic pole) width.
As an factor for determining the performance of a thin film magnetic head, there is an apex angle as represented by .theta. in FIG. 36A besides the throat height TH and the MR height MR-H and so on. The apex angle is an angle between a line connecting the corner of a side surface of the track surface of the photoresist films 113, 115 and an upper surface of the top pole layer 116.
To improve the performance of a thin film magnetic head, it is important to form the throat height TH, the MR height MR-H and the apex angle .theta. as shown in FIG. 36A precisely.
Especially these days, for enabling high surface density writing, that is to form a recording head with a narrow track structure, submicron measurement of equal to or less than 1.0 .mu.m is required for the track width P2W. For that, a technique for processing the top pole to submicron using a semiconductor processing technique is required. Further, utilizing magnetic materials which has high saturation magnetic flux density for the magnetic pole is desired following the implementation of the narrow track structure.
Here, the problem is that it is difficult to precisely form the top pole layer 116 on a coil area (apex area) being protruded like a mountain covered with photoresist films (for example, the photoresist films 113,115 shown in FIG. 36A).
As a method of forming the top pole, frame plating method, shown in, for example, Japanese Patent Application laid-open in Hei 7-262519, is used. When the top pole is formed by the frame plating method, first, a thin electrode film made of, for example, permalloy is formed all over the apex area. Next, photoresist is applied on it, and by patterning it through photolithography, a frame for plating is formed. Further, the top pole is formed through plating method having the electrode film formed earlier as a seed layer.
By the way, the apex area and other areas have, for example, equal to or more than 7 to 10 .mu.m differences in heights. If the film thickness of the photoresist formed on the apex area is required to be equal to or more than 3 .mu.m, a photoresist film of equal to or more than 8 to 10 .mu.m in thickness is formed in the lower part of the apex area since the photoresist with liquidity gathers into a lower area. To form a narrow track as described, a pattern with submicron width is required to be formed with a photoresist film. Accordingly, forming a micro pattern with submicron width with a photoresist film of equal to or more than 8 to 10 .mu.m in thickness is required. However, it has been extremely difficult.
Further, during an exposure of photolithography, a light for the exposure reflects by an electrode film made of, for example, permalloy, and the photoresist is exposed also by the reflecting light causing deformation of the photoresist pattern. As a result, the top pole can not be formed in a desired shape and so on since side walls of the top pole take a shape of being rounded. As described, with a related art, it has been extremely difficult to precisely control the track P2W and to precisely form the top pole so as to implement a narrow track structure.
For the reasons described above, as shown in a procedure of an example of a related art in FIGS. 33A and 33B.about.36A and 36B, a method of connecting the pole tip 110 and a yoke area-cum-top pole layer 116 after forming a track width of equal to or less than 1.0 .mu.m with the pole tip 110 which is effective for forming a narrow track of a recording head, that is, a method of dividing the regular top pole into the pole tip 110 for determining the track width and the top pole layer 116 which becomes the yoke area for inducing magnetic flux is employed (Ref. Japanese Patent Application laid-open Sho 62-245509, Sho 60-10409). By dividing the top pole into two as described, the pole tip 110 can be fine-processed to submicron width on a flat surface of the write gap layer 109.
However, there still exists problems as follows regarding the thin film magnetic head.
(1) First, in the magnetic head of a related art, the throat height is determined in an edge of a further side from the track surface 118 of the pole tip 110. However, if the width of the pole tip 110 becomes narrower, a pattern edge is formed being rounded by photolithography. As a result, the throat height which is required to have a highly precise measurement becomes inhomogeneous, which leads to a state where the throat height and the track width of magnetoresistive element becomes unbalanced in a procedure of processing and polishing the track surface. For example, when 0.5.about.0.6 .mu.m of the track width is needed, a problem in which an edge of a further side from the track surface 118 of the pole tip 110 is shifted from the throat height 0 position to the track surface 118 side and writing gap is widely opened, often causing a problem in which writing of recording data can not be performed.
(2) Next, as described above, in the magnetic head of a related art, it is not required to fine-process the top pole layer 116 as precise as the pole tip 110, since the track width of the recording head is determined by the pole tip 110 of the divided top pole. However, since the location of the top pole layer 116 is determined in the upper area of the pole tip 110 by positioning of photolithography, if both are largely shifted to one side when looking at the structure from the track surface 118 (FIG. 36A) side, so-called side write for performing writing on the top pole layer 116 side occurs. As a result, the effective track width becomes wider and a problem that writing is performed in a region other than the originally designated data recording region in a hard disk occurs.
Further, when the track width of the recording head becomes extremely finer, especially equal to or less than 0.5 .mu.m, a process precision of submicron width is required in the top pole layer 116. That is, if the measurement difference in a lateral direction of the pole tip 110 and the top pole layer 116 is too significant when looking at it from the track surface 118 side, as described above, a side write occurs and a problem that writing is performed in a region other than the originally designated data recording region in a hard disk occurs.
As a result, not only the pole tip 110 but also the top pole layer 116 is required to be processed to the submicron width, however, it is difficult to perform fine-process of the top pole layer 116 since there is a significant difference in heights as described above in the apex area under the top pole layer 116.
(3) Further, in the magnetic head of a related art, there is a problem that it is difficult to shorten a yoke length. That is, the narrower the coil pitch becomes, the easier the achievement of a head with short yoke length becomes and, especially, a recording head with a high frequency characteristics can be formed. However, when the coil pitch is made indefinitely small, the length of outer periphery end of the coil becomes a main factor for preventing the yoke length from shortening for the position of the throat height 0. The yoke length can be made shorter with two-layered coil than one-layered coil so that most of the recording heads for high frequency employ the two-layered coil. However, in the magnetic head of a related art, after forming a first layer of coil, a photoresist film of about 2 .mu.m is formed in order to form an insulating film between the coils. As a result, a small apex area having a rounded shape is formed in the outer peripheral end of the first layer of the coil. Next, a second layer of the coil is to be formed on it, however, etching to have a seed layer can not be performed in the slope of the apex area causing the coil to short-circuit, which makes it impossible to form the second layer of the coil. Accordingly, the second layer of the coil needs to be formed on a flat area. When the slope of the apex is 45.about.55.degree., if the thickness of the coil is 2.about.3 .mu.m and the thickness of the insulating film between the coils is 2 .mu.m, 8.about.10 .mu.m which is twice of 4.about.5 .mu.m, (the distance from the contact area of the top pole and the bottom pole to the outer peripheral end of the coil also needs to be 4.about.5 .mu.m) the distance from the outer peripheral end of the coil to the vicinity of the throat height 0 position is needed. This has been the main factor for preventing the yoke length from reducing. For example, when forming two layers of coils with 11 turns with line/space being 1.0 .mu.m/1.0 .mu.m, suppose the first layer is 6 turns and the second layer is 5 turns, then, the length of the coil of the yoke length is 11 .mu.m. Here, since 8.about.10 .mu.m is required in the apex area of the outer peripheral end, reduction of the yoke length to equal to or less than 19.about.21 .mu.m is impossible. This has prevented the high frequency characteristics from improving.